Multilayer getter structures and methods for making same

ABSTRACT

Getter multilayer structures are disclosed, embodiments of which include at least a layer of a non-evaporable getter alloy having a low activation temperature over a layer of a different non-evaporable getter material having high specific surface area, both preferably obtained by cathodic deposition. The multilayer NEG structures exhibit better gas sorbing characteristics and lower activation temperature lower than those of deposits made up of a single material. A process for manufacturing such structures includes depositing a first, high surface area NEG film on a support, and then depositing a thin over layer of low activation NEG film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Italian Patent Application No.MI2003A001178, filed Jun. 11, 2003, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

2. Field of the Invention

The present invention relates generally to getter materials, and moreparticularly to multilayer deposits including an over layer of lowactivation temperature getter alloy.

2. Description of the Related Art

Non-evaporable getter materials, also known in the art as NEG materials,include transition metals such as Zr, Ti, Nb, Ta, V, and alloys orcompounds thereof with one or more elements selected from Cr, Mn, Fe,Co, Ni, Al ,Y, La and other rare earth elements. Such alloys includebinary alloys such as Ti—V, Zr—Al, Zr—V, Zr—Fe and Zr—Ni, ternary alloyssuch as Zr—V—Fe and Zr—Co-rare earth elements, and other multi-componentalloys. They can also include metal compounds (e.g. metal oxides),non-metal, organics, etc. NEG materials are scavengers, removingselected species, typically gaseous, depending upon their compositionand operating conditions.

NEG materials are, for example, capable of reversibly sorbing hydrogenand irreversibly sorbing gases such as oxygen, water, carbon oxides and,in some cases, nitrogen. These materials are used for maintainingvacuum, as in, for example, evacuated interspaces for thermalinsulation. Getter materials are also used to remove the above-mentionedspecies from inert gases, primarily noble gases and nitrogen, forexample in gas-filled lamps or in the manufacture of ultrapure gasessuch as used in the microelectronics industry.

NEG materials can be employed in various forms, such as, for example,sintered pills or powders of the material within suitable containers. Insome applications, for reasons of available space or for simplicity ofconstruction, NEG materials are provided in the form of thin layers,generally tens or hundreds of microns (μm) in thickness, on an innersurface of an apparatus. Examples of uses of thin layers of NEG materialare disclosed in U.S. Pat. No. 5,453,659, which describes Field EmissionDisplays (known in the art as FEDs), wherein discrete and thin depositsof NEG material are formed among electron-emitting cathodes on theanodic plate of a display. U.S. Pat. No. 6,468,043 describes coating ofthe inner surface of pipes defining the chamber of a particleaccelerator with a NEG layer. U.S. Pat. Nos. 5,701,008 and 6,499,354describe, respectively, the use of getter materials in micromechanicaldevices and in miniaturized IR radiation detectors. Micromechanical ormicrooptoelectronic devices are known in the art as “micromachines” orMEMs (microelectromechanics). In all of these applications, the NEGdeposit (after activation) is employed at room temperature.

The functioning of NEG materials is based on reaction between the NEGmetal atoms and the above-mentioned gaseous species. As a result of suchreaction, oxide, nitride and/or carbide species are formed on the NEGsurface at room temperature, resulting eventually in the formation of apassivating layer that prevents further gas sorbing. This passivatinglayer can form rapidly in the presence of large amounts of gas, forexample at the first exposure to the atmosphere of the freshly producedNEG material, or during certain “dirty” manufacturing steps of thedevices in which the material is contained. The layer forms, althoughmore slowly, over time as a result of the normal functioning of the NEGin sorbing gaseous species.

At the beginning of its operating life, a NEG typically undergoes athermal activation treatment, normally under vacuum, whose object is themigration of passivating layer species towards the inside of thematerial structure, thereby exposing a fresh and active metallic surfacefor gas sorption. The activation may be complete, providing, forexample, a material surface essentially entirely made up of metal, orpartial, providing, for example, a “mixed” surface, made up of areas ofoxide-type species (or the like) and metallic areas. An activationdegree can be defined, corresponding to the fraction of “free” surfacesites, i.e. metals in the elemental state and consequently available forreaction with gases. In some cases, the activation treatment can beperiodically repeated during a device's operating life, in a processcalled reactivation, to restore the initial NEG gas sorbing properties.

In theory, complete activation of an NEG would generally be desirable,but it can be unfeasible in the manufacture of certain devices, due torestrictions on manufacturing times and/or heat sensitivity of theparticular device. Accordingly, partial activation is used for suchdevices, even though this results in lower gas sorbing properties andshorter NEG operating life.

The level of activation is dependent on process temperature and time;for example, an activation degree of 70% of a given material can bereached by treatment for 30 minutes at 350° C. or for 10 hours at 250°C., with the effect of temperature being greater than that of time. Theconditions of activation also vary according to the physicochemicalcharacteristics of the given material. For some materials, completeactivation can require very high temperatures. For example, completeactivation of an 84:16 Zr:Al alloy requires temperatures of at least700° C. and preferably about 900° C., unless extremely long times,typically unacceptable in industrial production, are used. Other alloys,such as some ternary Zr—V—Fe alloys, require much lower activationtemperatures and can be completely activated at about 350° C. in aboutone hour. As used herein, a “low activation temperature” material refersto a material (metal, intermetallic compound or alloy) which can beactivated to a high degree (e.g. about at least 90%) by a treatment ofone hour at a maximum required temperature of 300° C.

NEG deposits made up of a single metal (and particularly those oftitanium, which are the most commonly used) can be easily manufacturedby sputtering with open or porous morphology, which increases theeffective surface area and consequently the initial gas sorption rate.For an effective activation (or reactivation), however, pure metalsrequire comparatively high temperatures, generally higher than 450° C.In miniaturized devices such as FEDs or MEMs, wherein the NEG materialis quite close to functional or structural parts of the device, theactivation treatment can damage these parts. For example, in the case ofFEDs, in which the NEG is generally placed at the peripheric region,heating at 400° C. can compromise the tightness of sealing between thetwo glass parts forming the display, which are made up of a low-meltingglass paste. Similarly, exposure to these temperatures can compromisesealings between silicon components of MEMs, which are often composed ofbrazing alloys such as silver-based alloys or gold-tin or gold-indiumalloys.

Certain NEG intermetallic compounds or alloys have low activationtemperatures, for example about 300° C. or lower. However, the presentinventors have determined that these materials, when deposited bysputtering, give rise to thin layers having extremely compact morphologyand consequently a very reduced effective surface area, generallyequivalent to only a few times the deposit geometrical area. Thischaracteristic limits considerably the deposit sorbing properties atroom temperature, particularly its initial sorption rate and itscapacity. Such materials would require frequent reactivation, which maybe impractical or impossible in certain applications.

Accordingly, currently known NEG deposits obtained by sputtering eitherhave poor sorbing characteristics at room temperature (in particular, alow sorption rate) or require high activation temperatures incompatiblewith some applications, particularly in miniaturized devices. It wouldtherefore be desirable to provide NEG materials which are characterizedby low activation temperature and a large surface area.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a multilayer arrangementof non-evaporable getter materials, including a first or under layer ofnon-evaporable getter material having a relatively high surface areaand, upon the first layer, a relatively thin second or over layer of anon-evaporable getter alloy with low activation temperature. The layersare preferably obtained by cathodic deposition, with minimal exposure ofthe first layer to reactive gases occurring between the deposition ofthe two layers.

In one aspect of the present invention, a getter structure includes asupport, a first layer of a first non-evaporable getter having a highsurface area disposed over a surface of the support, and a second layerof a second non-evaporable getter having a low activation temperaturedisposed over the first layer. Preferably, the first layer and thesecond layer are cathodically deposited films. Also preferably, thesurface area of the first layer is equivalent to at least about 20 timesits geometrical area, and the second layer is no thicker than about 1μm.

A process for making a getter structure in accordance with an embodimentof the present invention includes depositing a first layer of anon-evaporable getter having a high surface area over a surface of asupport, and depositing a second layer of a second non-evaporable getterhaving a low activation temperature over the first layer. Preferably,the first layer and the second layer are films deposited by cathodicdeposition. Also preferably, the first layer is not exposed to gaseousspecies able to react therewith prior to the deposition of the secondlayer.

Advantageously, the multilayer structures of the invention provide alarge effective surface area and have a low activation temperature,providing great operating and activation efficiencies. This and otheradvantages of the present invention will become more fully apparent whenthe following detailed description of the invention is read inconjunction with the accompanying drawing(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a NEG multilayer structure in cross-section, in accordancewith one embodiment of the invention;

FIGS. 2 and 3 show, in cross-section, alternative embodiments of themultilayer of the invention;

FIG. 4 is a graph showing gas sorbing properties of exemplary multilayerdeposits of the invention and of a prior art NEG material; and

FIG. 5 is a graph showing gas sorbing properties of two exemplarydeposits of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

I. Multilayer Deposits

In one aspect, an embodiment of the invention provides a multilayerdeposit comprising at least a first layer (or “under layer”) and secondlayer (or “over layer”), as described further below. FIG. 1 is a linedrawing reproduction of a microphotograph of a multilayer in accordancewith one embodiment of the invention, seen in cross-section, as obtainedby scanning electron microscope.

The first layer, 11, of the multilayer deposit of the invention ispreferably formed on a support, 10. This support can be one that islater applied to the inner surface of the end use device. Preferably,however, the support 10 is the inner surface of the end use deviceitself, in the case of medium or small sized devices which can be putinto a sputtering chamber, such as FEDs or MEMs.

The first layer 11 preferably includes a NEG material that can bedeposited by sputtering in the form of a layer having a large surfacearea. Preferably, a metal selected from niobium, tantalum, vanadium,hafnium, and, more preferably, zirconium and titanium, is used. Alsopreferred are alloys such as described in U.S. Pat. No. 5,961,750,incorporated herein by reference, comprising zirconium, cobalt and oneor more elements selected from yttrium, lanthanum and other rare earthelements. Such alloys include alloys having the composition 80:15:5Zr:Co:A, where A represents one or more of Y, La and other rare earthelements.

The thickness of layer 11 can vary widely. Preferably, the thickness isat least about 0.2 μm, to ensure sufficient coverage of the support andsufficient surface area. Preferred minimum thickness is also determinedby the gas quantity that is expected to be sorbed. The maximum thicknessis typically determined primarily by production parameters, such as thetime necessary for layer growth, which generally dictates thicknesseslower than about 50 μm, for example between about 1 and 10 μm, if thesethicknesses are compatible with the required sorption capacity. However,greater thicknesses can be used.

The layer 11 has a relatively large surface area, determined by itsporosity. The porosity of such layers obtained by cathodic depositioncan be expressed as a ratio between the effective surface area and thegeometrical area. This ratio, indicated in the following as R_(e), is 1in the theoretical case of a perfectly smooth deposit, and increaseswith the increasing roughness or irregularity of the surface. For thepurposes of the invention, R_(e) is preferably greater than about 20 andmore preferably greater than about 50.

Over layer 11 there is formed by sputtering at least a second layer, 12,preferably made from a low activation temperature getter alloy,preferably having a composition differing from that of layer 11. As usedherein, a “low activation temperature” material refers to a materialwhich can be activated to a high degree (e.g. at least about 90%) by atreatment of about one hour at a maximum required temperature of about300° C. Of course, other definitions for “low activation temperature”will be apparent to those of skill in the art.

Preferred getter alloys for use in the second layer comprise Zr and V,and, optionally, one or more additional metals. For example, anexemplary getter alloy is ZrV₂. The additional metals may be selected,in some embodiments, from Fe, Ni, Mn, and Al, as described in U.S. Pat.No. 4,996,002; one such material is a getter alloy having thecomposition Zr 70%-V 24.6%-Fe 5.4% by weight, as described in U.S. Pat.No. 4,312,669. The additional metals may also be selected from yttriumand rare earth elements, such as lanthanum; one such material is agetter alloy having the composition 80%:15%:5% Zr:Co:A by weight,wherein A represents one or more elements selected from yttrium and rareearth elements, as described in U.S. Pat. No. 5,961,750. (In this case,the getter material of the first layer does not have this composition,and is preferably not a Zr:Co:A alloy.) The additional metal may also betitanium, as in a Zr—Ti—V alloy; one such alloy has the composition Zr44%-Ti 23%-V 33%, which can be activated (at least partially) by heatingfor just a few hours at 200° C.

It is noted that the term “alloy” (or getter alloy or NEG alloy) as usedherein can also include compositions corresponding to intermetalliccompounds, such as, for example, the ZrV₂ composition, since sputteringthin material layers of such compositions typically results in an almostamorphous or irregular structure typical of an alloy. “Alloy” can alsoinclude compounds of various metals, such as metal oxides.

The thickness of layer 12 is preferably not greater than 1 μm, and evenmore preferably ranges from 50 to 500 nm. At these thicknesses, thelayer retains the morphological characteristics of the underlying layer11, and consequently retains high R_(e) values and high sorption rate,while maintaining its low activation temperature properties.

The multilayer deposits of the invention are oriented in use such thatthe layer formed by the low activation temperature NEG alloy (i.e. thelayer 12 as described above) directly faces a space which is to beevacuated or wherein a gas to be purified is present. The second layer12 may directly contact such space, over its entire surface (as shown inFIG. 1), or it may be covered in whole or in part by a further layer, asdescribed below (FIGS. 2 and 3). Accordingly, the multilayer depositoptionally includes, on the upper surface of layer 12, a further layer,continuous or discontinuous, of palladium or of one compound thereof,such as palladium oxide, silver-palladium alloys comprising up to atomic30% of silver, and compounds or alloys of palladium and one or moremetals forming the getter material of layer 12.

For example, FIG. 2 shows an embodiment of the multilayer deposit havingan additional continuous layer of palladium (13). The palladium layer 13allows hydrogen selective sorption, as palladium, having high hydrogenpermeability, allows the transfer of this gas towards the underlyinggetter material layer (see e.g. PCT Pubn. No. WO 98/37958, incorporatedherein by reference). To maximize the hydrogen transfer rate to thegetter, the palladium layer is preferably no more than about 10 to 100nm in thickness, although greater or lesser thicknesses may be desirablein certain embodiments.

FIG. 3 shows another embodiment employing a discontinuous deposit ofpalladium (or a compound thereof). In this case, palladium (or apalladium compound) is present in the form of “islands” 14, 14′, 14″,etc. on the getter layer 12 surface; these islands cover preferably from10 to 90% of the layer 12 surface. Such a configuration is described inPCT Pubn. No. WO 00/75950, incorporated herein by reference, withreference to getter materials in the form of powders. The islands, notsorbing gases other than hydrogen, are not passivated and consequentlyact as passages for continuous hydrogen transfer into the getter alloy,whereas the remaining zones 15, 15′, etc. of the layer 12 surfacemaintain their usual operation as getters. This structure thereby actsas a constant hydrogen sorber and as a sorber of other gases followingsuitable activation.

Getter systems made up of a first material on which a second one isdeposited by sputtering are disclosed in PCT Pubn. NO. WO 02/27058,incorporated herein by reference. In the systems described therein,however, the underlying material is not obtained by sputtering, butrather is made up of a macroscopic body of sintered getter powders. Thepurpose of the deposit formed by sputtering on this macroscopic body isto reduce the loss of particles from the sintered material. The ratiobetween the volumes and the masses of the two components is such thatthe sputtered deposit has a negligible effect on the sorbing oractivation characteristics of the system. In addition, the underlyingmaterial is exposed to the atmosphere before the application of thedeposit layer by sputtering. As described below, the active layers ofthe deposits of embodiments of the present invention are preferablyformed by sputtering, and the first layer is not exposed to any gaseswhich would be reactive therewith (e.g. oxygen, nitrogen, water vapor,or carbon oxides) prior to application of the second layer.

II. Method of Preparing the Multilayer Deposits

In a further aspect, the invention provides a process for manufacturingmultilayer NEG structures. The process includes two subsequent steps ofdeposition by sputtering of two different materials. More particularly,the process of an embodiment of the present the invention comprisesfirst depositing by cathodic deposition on a support a first layer of anon-evaporable getter material, having a surface area equivalent to atleast 20 times its geometrical area; and then depositing by cathodicdeposition over said first layer a second layer, having a thickness notgreater than 1 μm, of a non-evaporable getter alloy having a lowactivation temperature. Preferably, between the two mentioned depositionsteps, the first layer is not exposed to gas species able to reacttherewith.

In particular, exposure of the first layer to oxidant species, such asoxygen or water, and thus passivation of the first layer, is preferablyavoided. This is readily achievable by carrying out the deposition ofthe first and second layer in succession in a chamber which is eitherevacuated or filled with an inert gas such as argon. This processprevents passivation of the first layer.

Although the invention if not limited to mechanism of operation oreffect, it is believed that the observed “transfer” of the lowactivation temperature of the second layer alloy to the underlying firstlayer material, which effect is demonstrated in the examples below, ispromoted by the non-passivated state of the first layer.

The support 10 on which the first layer 11 is deposited is typically aplanar support of metal, glass or silicon. The support may be placed,following layer deposition, into the final system at a suitableposition. Preferably, however, when the size and shape of the deviceintended for the getter deposit allow, the deposition occurs directly onan inner surface of the device itself This preferred manufacturingprocedure can be employed, for example, in the production of MEMs andFEDs.

A getter material layer 11, made up of a getter material as describedabove, is produced on the support by sputtering procedures known in theart. A typical sputtering procedure employs, in accordance with knownmethods, a vacuum chamber within which an electrical field can begenerated. The chamber contains a target (generally in the form of ashort cylinder) of the material to be deposited and a support on whichthe thin layer is to be formed. The chamber is evacuated and thenbackfilled with a noble gas atmosphere, generally argon, at a pressuregenerally from about 0.1 to 1.0 Pa. By applying a potential differenceof a few thousand volts between the stands of the support and of thetarget, so that the latter is at cathodic potential, a plasma of Ar⁺ions is created; these ions are accelerated by the electrical fieldtowards the target and cause its erosion through impact. The species(generally atoms or atoms clusters) derived from this target erosion aredeposited on the support, thus forming the thin layer. The deposit canentirely cover the support surface, obtaining a single continuousdeposit, or suitable maskings can be used to apply deposits to desiredregions of the support.

In a variation of this method, known as magnetron sputtering, a magneticfield is applied to the plasma region, confining the plasma andimproving the characteristics of cathode erosion and deposit formation.

In preparing the deposits of the invention, a first layer having highroughness or irregularity (and consequently the desired values of R_(e))is preferably prepared, by employing process parameters such as thefollowing. The support on which the deposition takes place is preferablycooled; in this way the atoms reaching the support have insufficientenergy to rearrange and form more regular structures, thus achieving akind of “quenching” of the deposit under formation. It is alsopreferable to operate at reduced currents, thus reducing the frequencyof impacts between Ar⁺ ions and the target and avoiding widespreadheating of the system. Finally, by positioning the target not directlyin front of the support, and/or by moving, rotating or vibrating thesupport during the deposition, the geometric disorder of the deposit canbe increased.

Layer 12 can be formed by sputtering from a target having the desiredcomposition, according to conventional procedures.

The optional deposit of palladium (or an alloy or compound thereof) canalso be formed by sputtering, which is preferable from the aspect ofconvenience, or by other known techniques such as chemical vapordeposition.

III. Properties of Multilayer Deposits

As discussed above, getter layers having low activation temperatures aredesirable. However, it has been found that monolayers of such getteralloys formed by sputtering tend to form compact layers havingundesirably low effective surface areas.

It has been further found, in accordance with the present invention,that a multilayer deposit having a high surface area first layer(underlayer) and a low activation temperature second layer (overlayer)presents the combined advantage of low activation temperature with higheffective surface area, as manifested in a high rate and capacity of gassorption at room temperature.

Exemplary multilayer deposits of the invention were prepared (Examples 1and 4) and compared with single layer deposits of either metal only(Example 3) or getter alloy only (Example 2) in room temperaturesorption tests (Example 5). The sorption of the multilayer deposits atelevated temperature (300° C.) was also evaluated, as described inExample 6. In each case, the sample was first activated byradiofrequency heating at 300° C. for 30 minutes

In the room temperature sorption tests, the species formed on the gettersurface as a result of gas sorbing do not have sufficient energy enoughto diffuse inwardly. The exhaustion of sorption capacity therefore showsthat all the metallic sites initially available on the surface aresaturated; accordingly, these tests are a measure of the starting numberof these surface sites. In the high temperature tests, the speciesinitially formed on the surface as a result of gas sorbing can diffuseinwardly; these tests therefore involve the entire amount of availablegetter material, and measure the entire capacity of the deposits.

As shown in FIG. 4, a multilayer deposit of the invention (designatedsample 1), having a first layer of titanium and a second layer of ZrV₂alloy, had room temperature surface sorption characteristics superior tothose of deposits of metal only (sample 3) or alloy only (sample 2) overthe entire range measured. In particular, the sorption rate and capacityof the invention multilayer deposit (curve 1) is greater by more than anorder of magnitude than those of the deposit of NEG alloy only (curve2), and at least double that of the deposit of titanium only (curve 3).

The difference in sorption rate and capacity of samples 1 and 3(multilayer vs. titanium only) can be attributed to an lower degree ofactivation achieved for the titanium (sample 3) than for the getteralloy-containing composition at the same activation temperature (300° C.in these tests). A lower activation degree corresponds to a lowersurface “cleanness”, resulting in a reduced number of sites availablefor gas sorbing.

The difference in sorption rate and capacity of samples 1 and 2, wherethe exposed surface of the deposit is made up of the same material (ZrV₂alloy), shows that the multilayer sample of the invention (sample 1) ischaracterized by a large specific surface, considerably greater thanthat obtainable depositing only the getter alloy (sample 2).

Sorption characteristics of the multilayer deposits at elevatedtemperatures are shown in FIG. 5. The two tested samples included atitanium underlayer and ZrV₂ overlayer, differing in that the sample ofcurve 5 (sample 1) included twice as much titanium as the sample ofcurve 4 (sample 4). As shown in the Figure, the two curves have the sameinitial sorption rate, confirming that at the beginning of the test thetwo samples are essentially equivalent in effective surface area andactivation degree. Sample 1, however, shows a total capacity about twicethat of sample 4, indicating that the titanium deposit underlying thealloy deposit takes part in gas sorption at the test temperature (300°C.).

From these analyses, it can be concluded that the multilayer deposits ofthe invention function as though they were a deposit of a singlematerial having desirable characteristics of the component layers; i.e.,the low activation temperature of the upper layer (layer 12) and thelarge effective surface area of the lower layer (layer 11). The latterproperty confers to the deposits high sorbing performances at roomtemperature which are not obtainable with deposits of getter alloysonly.

EXAMPLES

The following examples are intended to illustrate but not to limit theinvention.

Example 1 Preparation of a Multilayer Deposit Having Titanium Underlayer(3.3 μm) and ZrV₂ Over layer

This example provides an exemplary preparation of a double-layereddeposit according to the invention.

A polished monocrystalline silicon disc having a diameter of 2.5 cm wascleaned in an ultrasonic bath with an organic solvent (an alcoholicsolution of n-propylbromide) and subsequently rinsed in deionized water.This support was placed into a cathodic deposition chamber that cancontain up to three targets of different materials. The chamber wasevacuated to a pressure of 3×10⁻⁶ Pa, then backfilled with argon to apressure of 2 Pa. A titanium layer was first deposited, with thefollowing operating parameters:

-   -   power density on the target: 3.5 W/cm²;    -   target-support distance: 140 mm;    -   support temperature: 100° C.;    -   deposition time: 80 minutes.

Subsequently a second target of a ZrV₂ alloy was used, a layer of whichwas deposited on the titanium layer, employing a power density of 3W/cm², a deposition time of 10 minutes, and the target-support distanceand temperature given above.

The average thickness of the two layers was shown by electron microscopyto be 3.3 μm for the titanium layer and 0.2 μm for the ZrV₂ alloy. Thesethickness values (as all the thicknesses reported in the followingexamples) are average values.

This support having a two-layer deposit was designated sample 1.

Example 2 (Comparative) Preparation of ZrV₂ Alloy Deposit

The operating parameters described for the alloy deposition in Example 1are used to deposit a single layer ZrV₂ alloy, with the exceptions thatthe chamber was initially evacuated to 7×10³¹ ⁶ Pa, and the depositiontime was 60 minutes. The thickness of the deposit was shown by electronmicroscopy to be 3.5 μm.

This support having a one-layer deposit was designated sample 2.

Example 3 (Comparative) Preparation of Titanium Deposit

The operating parameters described for the alloy deposition in Example 1are used to deposit a single layer of titanium, with the exception thatthe deposition time was 90 minutes. The thickness of the deposit wasshown by electron microscopy to be 3.5 μm.

This support having a one-layer deposit was designated sample 3.

Example 4 Preparation of a Multilayer Deposit Having Titanium Underlayer(1.6 μm) and ZrV₂ Overlayer

The procedure of the Example 1 is repeated, with the exception that thetitanium deposition lasts 40 minutes. The average thickness of the twolayers was shown by electron microscopy to be 1.6 μm for the titaniumlayer and 0.2 μm for the ZrV₂ alloy.

This support having a two-layer deposit was designated sample 4.

Example 5 Room Temperature Gas Sorption of Monolayer and MultilayerDeposits

In this example, the gas sorbing properties at room temperature ofsamples 1, 2 and 3, prepared as described above, are evaluated.

The samples were mounted one at a time into a quartz bulb, which wasevacuated before every test through a turbomolecular pump to a residualpressure of 1×10⁻⁶ Pa, while heating at 180° C., which process tookabout 12 hours. The test sample was then activated by radiofrequencyheating at 300° C. for 30 minutes, through an induction coil placedoutside the bulb; the temperature was monitored with an opticalpyrometer. The test sample was then allowed to cool to room temperature,and the gas sorption test was carried out according to proceduresdescribed in the standard ASTM F798-82, i.e. introducing into the bulbcarbon monoxide, CO, at a pressure of 4×10⁻⁴ Pa and recording thepressure decrease downstream at known conductance.

The results of the sorption tests of the three samples, discussed above,are shown in FIG. 4, wherein the number of each curve corresponds to thenumber of sample as above indicated. The curves show the sample sorbingrate, S, measured in liters of gas sorbed every second per squarecentimeter of deposit (1/s×cm²), as a function of sorbed gas quantity,Q, measured in liters of gas sorbed, multiplied by the sorption pressure(in hectoPascal, hPa), divided by the deposit surface (hPa×1/cm²). Themaximum value of Q of the three curves measures the total samplecapacity.

Example 6 High Temperature Gas Sorption of Multilayer Deposits

In this example, the gas sorption properties at high temperatures ofsamples 1 and 4 are evaluated.

On a second sample prepared as described in Example 1, and on sample 4,CO sorption tests were carried out using procedures similar to thosedescribed in Example 5. The samples were activated by heating at 430°C., and the sorption tests were carried out at 300° C. The results arediscussed above and shown in FIG. 5. Curve 4 presents the data forsample 4, and curve 5 presents the data for the duplicate preparedaccording to Example 1.

While this invention has been described in terms of several exemplaryembodiments, it will be appreciated by those skilled in the art thatvarious alterations, permutations, additions, equivalents are within thetrue spirit and scope of the invention. It is therefore not intendedthat the invention be limited to the examples and embodiments disclosedherein but, rather, be giving the full spirit and scope of the presentinvention, as exemplified by the appended claims.

1. A multilayer non-evaporable getter structure comprising a first layerof a non-evaporable getter material having a surface area equivalent toat least 20 times its geometrical area, and directly contacting saidfirst layer, a second layer, having a thickness not greater than 1 μm,of a non-evaporable getter alloy having a low activation temperature. 2.The structure of claim 1, wherein said second layer fully covers saidfirst layer.
 3. The structure of claim 1, wherein the getter material ofsaid first layer is selected from the group consisting of zirconium,titanium, niobium, tantalum, vanadium, hafnium, and Zr—Co—A alloys,wherein A represents one or more elements selected from yttrium and rareearth elements.
 4. The structure of claim 1, wherein the thickness ofsaid first layer is between about 0.2 and 50 μm.
 5. The structure ofclaim 4, wherein said thickness is between about 10 and 20 82 m.
 6. Thestructure of claim 1, wherein the surface area of said first layer isequivalent to at least about 50 times its geometrical area.
 7. Thestructure of claim 1, wherein the getter alloy of said second layercomprises Zr and V.
 8. The structure of claim 7, wherein said getteralloy further comprises smaller quantities of one or more elementsselected from Fe, Ni, Mn, and Al.
 9. The structure of claim 8, whereinsaid getter alloy has a composition by weight of about Zr 70%-V 24.6%-Fe5.4%.
 10. The structure of claim 1, wherein the getter alloy of saidsecond layer has the composition of about 80%:15%:5% Zr:Co:A by weight,wherein A represents one or more elements selected from yttrium and rareearth elements, and the material of said first layer is different fromthat of said second layer.
 11. The structure of claim 10, wherein saidfirst layer is not a Zr:Co:A alloy.
 12. The structure of claim 7,wherein the getter alloy of said second layer is a Zr—Ti—V alloy. 13.The structure of claim 12, wherein the getter alloy of said second layerhas the composition of about Zr 44%-Ti 23%-V 33%.
 14. The structure ofclaim 7, wherein the getter alloy of said second layer is ZrV2.
 15. Thestructure of claim 1, wherein the thickness of said second layer isbetween about 50 and about 500 nm.
 16. The structure of claim 1, furthercomprising a continuous or discontinuous layer of palladium or acompound thereof, deposited on the surface of said second layer opposedto the surface in contact with said first layer.
 17. The structure ofclaim 16, wherein said palladium compound is selected from palladiumoxide, silver-palladium alloys comprising up to about 30 atom % ofsilver, and compounds of palladium with one or more metals forming thegetter material of the second layer.
 18. The structure of claim 16,wherein said layer of palladium or a compound thereof is discontinuousand covers from about 10 to about 90% of the second layer surface. 19.The structure of claim 16, wherein said layer of palladium or a compoundthereof has a thickness between about 10 and about 100 nm.
 20. A processfor manufacturing a multilayer structure comprising: depositing bycathodic deposition on a support a first layer of a non-evaporablegetter material having a surface area equivalent to at least 20 timesits geometrical area, and depositing by cathodic deposition over saidfirst layer at least a second layer, having a thickness not greater than1 μm, of a non-evaporable getter alloy having a low activationtemperature; such that, between the two deposition steps, the firstlayer is not exposed to gaseous species able to react therewith.
 21. Aprocess according to claim 20, wherein the cathodic deposition of saidfirst layer comprises (a) cooling the support, (b) operating at lowcurrent values, (c) operating with the target not directly placed infront of the support, (d) moving, rotating or vibrating the supportduring the deposition, or any combination thereof.
 22. A getterstructure comprising: a support; a first layer of a first non-evaporablegetter having a high surface area disposed over a surface of saidsupport; and a second layer a second non-evaporable getter having a lowactivation temperature disposed over said first layer.
 23. A getterstructure as recited in claim 22 wherein said first layer and saidsecond layer are cathodically deposited films.
 24. A process for makinga getter structure comprising: depositing a first layer of anon-evaporable getter having a high surface area over a surface of asupport; and depositing a second layer of a second non-evaporable getterhaving a low activation temperature over said first layer.
 25. A processfor making a getter structure as recited in claim 24 wherein said firstlayer and said second layer are films deposited by cathodic deposition.